﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Sockets;
using System.Net;
using System.Runtime.InteropServices;
using System.Text;
using System.Data;
using System.Configuration;
using System.Web;
using System.Xml;

namespace SystemTimeCalibration
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("正在校准时间，By:WiMi");
            SystemHelper.SetLocalMachineTime(GetNetworkTime());
            Console.WriteLine("完成校准时间，By:WiMi");
        }

        /// <summary>
        ///
        /// </summary>
        internal struct SYSTEMTIME
        {
            public ushort wYear;
            public ushort wMonth;
            public ushort wDayOfWeek;
            public ushort wDay;
            public ushort wHour;
            public ushort wMinute;
            public ushort wSecond;
            public ushort wMilliseconds;

            /// <summary>
            /// 从System.DateTime转换。
            /// </summary>
            /// <param name="time">System.DateTime类型的时间。</param>
            public void FromDateTime(DateTime time)
            {
                wYear = (ushort)time.Year;
                wMonth = (ushort)time.Month;
                wDayOfWeek = (ushort)time.DayOfWeek;
                wDay = (ushort)time.Day;
                wHour = (ushort)time.Hour;
                wMinute = (ushort)time.Minute;
                wSecond = (ushort)time.Second;
                wMilliseconds = (ushort)time.Millisecond;
            }
            /// <summary>
            /// 转换为System.DateTime类型。
            /// </summary>
            /// <returns></returns>
            public DateTime ToDateTime()
            {
                return new DateTime(wYear, wMonth, wDay, wHour, wMinute, wSecond, wMilliseconds);
            }
            /// <summary>
            /// 静态方法。转换为System.DateTime类型。
            /// </summary>
            /// <param name="time">SYSTEMTIME类型的时间。</param>
            /// <returns></returns>
            public static DateTime ToDateTime(SYSTEMTIME time)
            {
                return time.ToDateTime();
            }
        }
        internal class Win32API
        {
            [DllImport("Kernel32.dll")]
            public static extern bool SetLocalTime(ref SYSTEMTIME Time);
            [DllImport("Kernel32.dll")]
            public static extern void GetLocalTime(ref SYSTEMTIME Time);
        }

        public class SystemHelper
        {
            public static void SetLocalMachineTime(DateTime dt)
            {
                //转换System.DateTime到SYSTEMTIME
                SYSTEMTIME st = new SYSTEMTIME();
                st.FromDateTime(dt);
                //调用Win32 API设置系统时间
                Win32API.SetLocalTime(ref st);
            }
        }

        /// <summary>
        /// 获取NTC时间
        /// </summary>
        /// <returns></returns>
        public static DateTime GetNetworkTime()
        {
            int i = 0;
            while (true)
            {
                i++;
                Console.WriteLine("尝试第" + i.ToString() + "次，By:WiMi");
                //default Windows time server
                string ntpServer = "cn.pool.ntp.org";

                // NTP message size - 16 bytes of the digest (RFC 2030)
                var ntpData = new byte[48];

                //Setting the Leap Indicator, Version Number and Mode values
                ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)

                var addresses = Dns.GetHostEntry(ntpServer).AddressList;

                //The UDP port number assigned to NTP is 123
                var ipEndPoint = new IPEndPoint(addresses[0], 123);
                //NTP uses UDP
                var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

                socket.Connect(ipEndPoint);

                //Stops code hang if NTP is blocked
                socket.ReceiveTimeout = 3000;

                socket.Send(ntpData);
                socket.Receive(ntpData);
                socket.Close();

                //Offset to get to the "Transmit Timestamp" field (time at which the reply
                //departed the server for the client, in 64-bit timestamp format."
                const byte serverReplyTime = 40;

                //Get the seconds part
                ulong intPart = BitConverter.ToUInt32(ntpData, serverReplyTime);

                //Get the seconds fraction
                ulong fractPart = BitConverter.ToUInt32(ntpData, serverReplyTime + 4);

                //Convert From big-endian to little-endian
                intPart = SwapEndianness(intPart);
                fractPart = SwapEndianness(fractPart);

                var milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);

                //**UTC** time
                var networkDateTime = (new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc)).AddMilliseconds((long)milliseconds);

                return networkDateTime.ToLocalTime();
            }
        }

        // stackoverflow.com/a/3294698/162671
        static uint SwapEndianness(ulong x)
        {
            return (uint)(((x & 0x000000ff) << 24) +
            ((x & 0x0000ff00) << 8) +
            ((x & 0x00ff0000) >> 8) +
            ((x & 0xff000000) >> 24));
        }
    }
}
